No description available.

Many species from economically important genera remain rooting recalcitrant, prohibiting the commercialisation of many species in forestry and horticulture, and hindering genetic improvement by conventional breeding or recombinant DNA technology, where vegetative propagation is often used to preserve the genetic fidelity of elite progeny. Two cherry species (Prunus avium and P. padus) were used as models in this study to investigate the physiological and genetic manipulation of adventitious rooting. Mature trees are typically more difficult to propagate vegetatively than their juvenile counterparts. For some trees, micropropagation can circumvent certain effects of ageing and maturation, restoring shoot vigour and rooting, but the mechanism(s) involved have not been elucidated. During micropropagation, subculture interval was found not to be the predominant factor promoting the 'apparent rejuvenation' of mature P. avium tissue. 'Apparently rejuvenated' ex vitro and hedged (putatively) mature P. avium trees were treated with gibberellins predicted to have a range of structural related activities. GA, improved the rooting of cuttings from hedged (putatively) mature cherry, but not from ex vitro trees. Methodology to regenerate adventitious shoots from P. avium leaf explants was developed, (putative) transgenic P. padus plants were produced by an Agrobacterium tumefaciens mediated strategy. Auxin redistribution in planta is postulated to require a component of active transport; inhibition of the predominantly basipetal transport has profound effects on rooting. The putative function of the Arabidopsis thaliana AtAUX1 gene is that of a cellular auxin influx carrier, possibly, as described by the chemiosmotic hypothesis. This thesis examined the hypothesis that transformation with the AtAUX1 gene would enhance the delivery of the root-inducing signal to improve rooting of P. padus, a species which is rooting recalcitrant and more or less obligate on exogenous auxin for this process. However, all six, constitutively expressed, Cauliflower Mosaic Virus 35S promoter driven, 35S::AtAUX1, transgenic shoot lines had reduced rooting.

Thesis (B.A.)--Haverford College, Dept. of English, 2007. / Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--Washington State University, May 2007. / Includes bibliographical references.

The meiotic behaviour and pollen fertility of Lambert sweet cherry (Prunus avium L.) and irradiation propagates of Lambert were investigated. Chromosome clumping, due to associations between the centromere region of non-homologous chromosomes, characterized early meiotic stages in Lambert. While the associations, which were evident as chromatic centers, complicated interpretation of pachynema, the pachytene morphology of the eight chromosomes was described. Except for small chromatic areas delimiting the centromere, all chromosomes were basically achromatic. Three chromosomes had an additional one or two chromatic regions, which in all cases were in the short arm. One chromosome, designated number 3, had a major heterozygous interstitial deletion in the short arm. Marked repulsion between the homologous chromosomes during diplonema resulted in a diffuse stage. The single pair of univalents, occasionally observed throughout meiosis and considered to be of desynaptic origin, were first detected in diplonema. Subsequent meiotic stages were usually normal, and the incidence of abnormal meiosis and tetrad stages containing micronuclei were estimated to be 9-62 per cent and 3.24 per cent respectively. Meiosis was characterized by synchronous division within the anther locules. Cytoplasmic connections were evident between neighbouring meiocytes during meiosis I, and cytomictic phenomena were observed occasionally. Abortion of 50 per cent of the developing microspores occurred prior to the first mitotic division of the spore nucleus, and was attributed to the heterozygous deletion in chromosome 3. Pollen abortion at anthesis was estimated to be about 42 per cent. Annual or regional effects on the incidence of abnormal meiosis or pollen abortion were not evident. Forcing of blossom buds at 15°C did not appear to affect meiotic behaviour. Twelve irradiation propagates of Lambert were investigated. Of these, seven had pollen fertility similar to the parental Lambert clone, and their meiotic behaviour also was comparable. The remaining five propagates had reduced pollen fertility. One propagate was found to have a greatly increased incidence of the single pair of univalents, as compared to parental Lambert; two propagates contained a reciprocal translocation; and two contained a paracentric inversion. The extent of pollen abortion was predictable from the meiotic behaviour in only one of the latter five propagates. Pollen studies revealed significant annual variation among the 12 irradiation propagates, some varying more than others. With one exception, forcing of blossom buds at 15°C did not appear to affect meiotic behaviour. / Land and Food Systems, Faculty of / Graduate

Three species or varieties of chokecherry reportedly grow in North America. Data were collected to determine if the varieties could be distinguished by morphological characteristics of the seedling. Seeds, collected from 20 locations in North America, were grown in a greenhouse where gross environmental factors could be controlled. For two growing seasons, data were collected on (1) height, (2) leaf thickness, (3) rate of root growth, (4) number of teeth, (5) number of leaves, and (6) the ratio of leaf length to width. The resulting data were subjected to analysis of variance and group means, and correlation studies. For the most part morphological variations within population were greater than the variation between populations. Where significant differences did exist between populations, patterns could not be determined; consequently, it was not possible to distinguish varieties of chokecherry seedlings by those morphological characteristics observed in this study. It was concluded that there is only one species of chokecherry in North America with numerous local variations or biotypes.

No description available.

Thesis (MScAgric (Horticulture))--Stellenbosch University, 2008. / Sweet cherries (Prunus avium L.) have a high chilling requirement and grow best in areas receiving >1 100 Utah chill units during winter. The main production areas in South Africa, and particularly the eastern Free State, frequently receive insufficient winter chilling and late spring frosts leading to problems of poor budburst, flowering, floral abnormalities and poor fruit set. Research was conducted on the cultivar ‘Bing’ to determine the main factors causing its low fruit set. Various trials were conducted to optimize the timing of rest breaking agents, identify suitable cross pollinizers that flower synchronously with ‘Bing’, and evaluate the influence of temperature and pollen-pistil interactions on fertilization and fruit set. Pollen biology studies using 2- to 3-year-old ‘Bing’ sweet cherry trees were conducted near Clarens, eastern Free State, during the 2005 and 2006 seasons to determine the most suitable cross pollinizer/s for ‘Bing’ and to assess the influence of temperature and pollen-pistil interactions on pollen tube growth and ovule longevity. Significant differences in pollen germination (‘rates’ deleted) occurred between pollinizers, although differences were noted in pollen performance on the stigma and style (in vivo) compared to the artificial media (in vitro), indicating a lack of correlation between in vitro germination and in vivo pollen-pistil interactions. Pollen tube growth, following cross pollination, was influenced by pollinizer genotype, temperature, and the number of pollen grains deposited on the stigma. The highest pollen tube growth rates in ‘Bing’ styles were recorded for the pollinizers ‘Black Tartarian’ (2006), ‘Lapins’ and ‘Rainier’ sweet cherry cultivars at temperatures of approximately 21°C. Temperature had the most significant influence on ovule longevity with the lower orchard temperatures extending ovule viability compared to the higher laboratory temperatures, although pollen tube growth rates were also reduced, thus shortening the effective pollination period. Cross pollination was also shown to extend ovule viability. The results indicate that ‘Black Tartarian’, ‘Lapins’ and ‘Rainier’ were the most suitable pollinizers for ‘Bing’. Hand-pollination with pollen from these donors resulted in a several-fold increase in seed set over naturally-pollinated control flowers. It appears that the principle factors causing poor fruit set in ‘Bing’ sweet cherry are premature abortion of the ovule before fertilization and inadequate transfer of sufficient viable pollen under orchard conditions. Rest breaking trials were conducted on 4-year-old ‘Bing’ sweet cherry trees on ‘Gisela® 5’ rootstock near Clarens (28°28’S; 28°19’E, 1860m) and Reitz (28°0’S; 28°28’E; 1717m) in the eastern Free State, South Africa, during the 2005 and 2006 seasons respectively. In 2005 five treatments were evaluated; viz. 1% and 2% Dormex® (hydrogen cyanamide, HCN); 1% Dormex® + 3% mineral oil; and 3% Lift® (thidiazuron and mineral oil) sprayed at three dates (29 July 2005, 5 August 2005 and 12 August 2005) preceding expected the “green-tip” stage of flower development, plus an unsprayed control. In 2006 four treatments were evaluated; viz. 1% Dormex®; 1% Dormex® + 3% mineral oil; 3% Lift® applied on three dates (26 July 2006, 7 August 2006 and 12 August 2006) and an unsprayed control. No interaction was observed between time of application and type of rest breaking agent (RBA). RBAs were effective at improving budburst and yield during both seasons with the time of application of RBAs having the most significant influence on budburst and production efficiency in ‘Bing’ sweet cherry trees. RBAs were most effective at improving vegetative budburst when applied 9 to 16 days before the (‘actual’ deleted) “green-tip” stage of flower development. Floral budburst and yield were increased by 1% Dormex® + 3% mineral oil and 3% Lift®, but results varied between seasons indicating that time of RBA application should be based on chilling accumulation and bud development stage and not based on calendar date. This current research suggests that ‘Bing’ sweet cherry is poorly suited climatically to the current production areas of the eastern Free State and short-term research needs to identify methods of improving chilling and fruit set by means of evaporative cooling and fruit set-enhancing plant growth regulators. Longer term work requires the identification of new, lower chill cultivars with improved climatic adaptation to South African conditions.

No description available.